1. Field of the Invention
The present invention relates to polyisocyanates containing uretdione groups and having more than two terminal, partially or fully blocked isocyanate groups, to processes for their preparation and to their use in polyurethane coating systems.
2. Discussion of the Background
Polyisocyanates, which especially are used in polyurethane powder coatings, which contain uretdione groups, are known as described, in particular, in DE-A 30 30 554. Such polyisocyanates, however, have only two terminal, partially or fully blocked isocyanate groups and are strictly linear in structure. As disclosed in EP-A-254 154 (page 2, column 1, line 63 to end of sentence), this fact is of great disadvantage in practice. A need, therefore, continues to exist for a polyurethane which contains uretdione groups, which exhibits improved properties for use in powder coatings.